Overview

Brief Summary

Biology

The Lulworth skipper is single-brooded; adults fly between late June and late September, and eggs are laid in small groups in flower sheaths of tall patches of tor-grass. After hatching three weeks later, the larvae spin a cocoon in which to hibernate. They emerge the following spring and create tubes in which to live by spinning the leaf together. Pupation occurs amongst the clumps of tor-grass (2).

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Description

The Lulworth skipper is one of our smallest butterflies (3). Males are orange-brown with light spots and a black band on the forewings. Females are darker in colour than males and do not have this dark band. The underside of both sexes is orange-brown with no markings or spots (1). The caterpillar reaches 2.4 centimetres in length, has a green body with a darker green, yellow-bordered line along the back and pale yellow lines along the sides (2).

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Distribution

Range

Found in some areas of south and central Europe, Asia Minor and North Africa. In Britain the Lulworth skipper is largely restricted to coastal areas of south Dorset, centred on the village of Lulworth, colonies are also known from the Isle of Portland and west Dorset (3).

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Threats

The Lulworth skipper was once found in Devon. Apart from the loss of the species in this area, its range has stayed relatively stable. Its habitats in Britain have not been destroyed, largely because the slopes on which the species occurs are too steep to be ploughed or occur in military training areas. During the twentieth century, the levels of grazing in areas inhabited by this skipper have decreased; the foodplant has been able to grow to the taller heights that suit this species as a result. Small declines in the Lulworth skipper have occurred in some areas due to an increase in grazing (4).

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Management

Conservation

Scrub removal has benefited the species in some localities, and many sites are ungrazed (4). However, research has indicated that some grazing may actually benefit this butterfly, as nectar-source flowers will be encouraged, but grazing in spring and summer when the larvae tend to be located at high points on vegetation is detrimental. Maintaining the longer sward needed by this species conflicts with conservation management for other butterfly species such as the Adonis blue butterfly (Lysandra bellargus); conservation measures will therefore need to manage different parts of an area for different species, with the Lulworth skipper becoming a priority in the existing key areas (3).

The species occurs locally across Central Europe, Asia Minor and North Africa, where its population is considered stable. Its numbers have declined in Northern Europe, leading to its European status of "vulnerable".[1] Its range in Britain is restricted to the south coast of Dorset, however it is locally abundant and its numbers currently are perhaps at their greatest since its discovery there.[2]

With a wingspan of 24 to 28 millimetres, females being larger than males, the Lulworth skipper is a small butterfly, the smallest member of the Thymelicus genus in Europe and among the smallest butterflies in Britain. Aside from the size difference, the sexes are distinguished by females having a distinct circle of golden marks on each forewing. Due to their likeness to the rays around the eye of a peacock's feather, these are often known as "sun-ray" markings, and they can faintly appear on males.

Contents

The Lulworth skipper was first described by German entomologistS. A. von Rottemburg in 1775.[3] The butterfly was first discovered in Britain on 15 August 1832, when specimens were taken from Lulworth Cove in Dorset by English naturalist James Charles Dale[3] It was introduced the following year as the Lulworth skipper (Thymelicus acteon), a name that has remained unchanged; it is the only one of Britain's vernacular butterfly names for which there has never been a proposed substitute.[3][4]

The male Lulworth skipper has a wingspan of 24 to 27 millimetres (0.94 to 1.06 in), and the female 25 to 28 mm. This makes it one of Britain's smallest butterflies and, in Europe, the smallest member of the Thymelicusgenus.[5] Of Britain's five "golden" skippers—the others being the silver-spotted skipper (Hesperia comma), large skipper (Ochlodes sylvanus), small skipper (Thymelicus sylvestris) and Essex skipper (Thymelicus lineola)—the Lulworth is both the smallest and darkest.[2] Beyond its small size, it is distinguished particularly by its dark, dun-coloured wings that appear with tinges of olive-brown; this darkening especially apparent in males.[6]

Variations are known to occur; in north-west Africa, the uppersides of the fore and hind wing are darker, with hints of greenish or greyish brown.[7] Similarly-coloured races occur in Spain, Elba, Crete, and other Eastern Mediterranean islands. T. acteon christi, endemic to the Canary Islands, displays colour variations, with the uppersides of the fore-wing showing defined yellow–orange markings.

The butterfly is sexually dimorphic;[3] females have a distinct circle of golden marks on each forewing, often called "sun-ray" markings due to their likeness to the rays around the eye of a peacock's feather.[6] Males sometimes have these markings, though they are noticeably fainter (see Illustration 1).

In Great Britain, where the butterfly reaches the northern limit of its range, its distribution is restricted to the southern coastline of the county of Dorset.[9][10] Here, both the population and range have changed little in recent decades; it is locally abundant, with the majority of colonies found on the coast between Weymouth and Swanage and on the Purbeck Ridge, a line of inland chalk hills. Two outlying colonies also exist, at Burton Bradstock and on the Isle of Portland; the cause of the colony on Portland is unknown, but has been put down to either natural colonisation or released specimens.[b] There is evidence to suggest that the Lulworth skipper is now more abundant in Dorset than at any other time since its discovery in 1832.[2]

Although colonies of Lulworth skippers existed in Devon, the species has, beyond single records, not be seen in the county since the 1930s. Similarly, records of occurrences exist for Cornwall, but they have not been verified as native colonies.[7][11]

Habitats are primarily on unfertilised calcareous grassland; this includes chalk download, coastal grassland and undercliffs in Britain. In all of these habits Tor-grass (Illustration 2), the butterfly's sole food plant and that on which it lays eggs,[12] is widespread. Tall, ungrazed grass is a favoured habitat due to oviposition and larval development; Lulworth skippers have benefited from the move away from tight grazing by sheep in the last century and recently outbreaks of myxomatosis among rabbit populations, which otherwise maintain a lower grass height.[2][3][11] However, there is evidence to suggest that minimal grazing is not detrimental to the species, and may in fact be beneficial in that it encourages the growth of flowers that act as adult nectar sources.[6]

The females lay their eggs in rows of 5 to 6 (although as many as 15 have been recorded[2]) on the flower-sheath of Tor-grass (Brachypodium pinnatum), preferring the dead sheaths of tall plants.[13] The care taken by females over where to lay their eggs is considered the only remarkable part of the Lulworth skipper breeding process, otherwise it is considered common.

Upon hatching, the 2.5 cm (1 in) long larva spins a compact cocoon on the site of the eggshell.[2] In this, it will overwinter until around the third week of April,[13] at which point it will eat its way out by making a small hole in the side of the sheath.[2] The caterpillar will then search for tender Tor-grass blades and feed upon them by chewing out notches from the margin. During this time, it will live separately, within a tube composed of the two edges of a blade bound by cords of silk.[2] Fresh tubes will be made as the caterpillar grows larger.[13] Lulworth skipper caterpillars live in the warmest zone of a grass clump, at a height of 20 to 40 centimetres (8 to 16 in).[2]

The pupal stage lasts for about two weeks, from the beginning of June onwards, until late July.[13] It is formed inside a loose "nest" of silk and grass that is spun deep inside a tussock of tor grass. Imago begin to emerge in the early middle of July and finish emerging in the middle of September. Typically, they will live for five to ten days—the normal lifespan for a non-hibernating butterfly of the Lulworth's seasonal stage. They fly only in strong sunshine and tend to form discrete colonies,[2] with the largest containing up to 100,000 individuals.[6][11]

A graph illustrating the life cycle of the Lulworth skipper in Great Britain; in other parts of the world, the life cycle varies, with adults usually emerging earlier in the season.[2][13]

^Lulworth skipper adults rarely stray from their favoured breeding areas and are considered poor migrants.[2][6] This is demonstrated by other regions of Britain, containing tor-grass in abundance, where there are no recorded colonies. Any migration to and natural colonisation of Portland would have meant travel across open water, casting further doubt upon the idea. Dispersal must occur, however, as sites such as restored grassland at Durlston and the area between Burton Bradstock and Weymouth have been colonised.[6]